Many types of fuel injection systems for internal combustion engines have been developed over the years. Common rail fuel injection systems are well known and widely used in connection with multi-cylinder internal combustion engines. A typical common rail fuel system includes a low pressure fuel source, a high pressure pump and a common rail connecting the high pressure pump with a plurality of fuel injectors. Injection of fuel at rail pressure can occur relatively precisely by electronically controlling each of the fuel injectors coupled with the common rail. Common rail systems have seen widespread success in part because they provide a relatively simple and straightforward means for providing fuel to a plurality of fuel injectors, and enable injection of fuel at relatively precise times and injection amounts. Common rail systems have also proven to be a relatively efficient and effective way to handle relatively high fuel pressures. While known common rail systems have long served as an industry standard for high pressure fuel injection practices, there is room for improvement.
On the one hand, containing a volume of highly pressurized fuel can be relatively difficult, requiring specialized hardware such as seals and plumbing. Parts subjected to extremely high pressures may also have a tendency to wear relatively more quickly than parts used in lower pressure environments. It can also require significant engine output energy to maintain a relatively large volume of fuel at high pressure. Relying solely upon a common rail as a pressure source for fuel can ultimately impact engine efficiency.
Systems have been proposed where a common rail is used to supply fuel at a first pressure to a plurality of fuel injectors of an engine system. A hydraulically actuated or cam actuated pressure intensifier may also be used in such systems to enable fuel injection at selective times at a higher pressure. United States Patent Application Publication No. 2006/0243253 to Knight proposes incorporating a cam actuated piston to a common rail system to enable injection of fuel at rail pressure from the common rail, or at a higher pressure from the pressure intensifier. In Knight's system, the cam actuated pressure intensifier is also used to assist in maintaining the pressure of the common rail when it is not being used to directly elevate fuel pressure for an injection. As a result, the piston in Knight will apparently pump at high pressure continuously. Continuously subjecting components of the fuel system to high pressure from the piston in Knight may result in excessive leakage between and among certain components. Leakage of high pressure fuel as in Knight would tend to waste energy, as the engine output energy used to pressurize the leaked fuel cannot readily be recovered.